My World lost 90% of my buildings and all my items disappeared, from diamond to cobblestone. But I spawn where my bed used to be.

I logged on, and my acount name was 'Steve' when it is normally 'Epic3159' and I spawned with a clear inventory where my house used to be. That had completely dissapeared, as had all my items within it, plus all the building I had spent the last 30 hours on - from underground tunnels to forts on the mountain. All dissapeared, except for 10%, i.e. half a fort tower on a mountain and part of a tunnel i had dug into the ground to mine minerals.

There is no logical order to what was lost, for instance my house was the first thing i built, the fort was the last thing i built, and both have dissapeared but something the tunel i built half way through (in terms of game time) was still there - so its not a file that has been reset to 20 hours ago, but definitley a bug.